Fadkiller is a massively inflated Announcer head with the rest of the body all deflated to be invisible.
Fadkiller is an Announcer clone made the way she is in a secret laboratory under Well, sent out into the world to hunt down the other Freaks. Being incredibly powerful, implacable to the end and nearly-impossible to kill, she seems to be the bane of the other GMod Monsters and, therefore, is avoided like the plague. She also is seemingly unable to be hindered, let alone stopped, by the Watcher, making her a force to be reckoned with.
It is rumored that the real origin of Fadkiller was like this: Fadkiller was once a regular Announcer that was riding in a commuter train cab car when it crashed into the back of a train carrying toxic waste, instantly killing her. Her body was given to the secret laboratory and was tested, however, someone inserted Australium into her body, thus creating Fadkiller.
Fadkiller is capable of firing lasers from her mouth at anything she can see. She can also summon a Portal elevator that acts as a teleporter to take her long distances. Fadkiller is also made to be incredibly hard to defeat even by GMod Monsters of the greatest power. This has put her in a deity-like position similar to Snyphurr, only where Snyphurr is neutral-ish and assists the wielder of Doc Jarate's Bugle, Fadkiller is greatly malevolent to all.
Without her elevator teleporter, Fadkiller is rather slow. She's also unable to open things such as doors and boxes. Because of this she will destroy any doors seen, but for some reason ignores boxes and dressers making them excellent places to hide. There is also simply something that Fadkiller gives off into an area's setting that is easily detected by GMod Monsters, acting as a warning sign of her proximity.